This invention relates to a method of bonding a lead of film carrier or the like and a semiconductor element.
The method of connection between a film-shaped lead and an aluminum electrode on a semiconductor element by way of a metal bump (so-called film carrier method) is employed as a mounting method suited to thin or small structure. Referring to FIGS. 2A, 2B, the bonding method of film lead and electrode on semiconductor of the conventional film carrier type is described below. By etching an electrode 2 on a semiconductor element 1 and a Cu foil adhered to film 3a of a film carrier 3, they are positioned with an Zn-plated lead 4. At this time, metal bumps 5 may be formed either on the electrode 2 on the semiconductor element 1 by way of a multilayer metal film (barrier metal), or on the lead side by transfer bump method. FIG. 1 shows the formation of metal bump on the lead side by the transfer bump method. The semiconductor element 1 is placed on a state 24, and is pressurized and heated 23 from above the lead 4 on the surface of semiconductor element by a bonding tool 20 having a heater 21. Next, when pressure-heating 23 is removed, if the metal bump 5 is made of Au, the metal bump 5 and the aluminum electrode 2 on the semiconductor element 1 are joined with Au-Al alloy. The temperature of the bonding tool 20 reaches 350.degree. to 550.degree. C.
In such bonding, since the temperature of the bonding tool is relatively high, the bottom of the bonding tool 20 and the lead 4 are fused together when pressurizing and heating as shown in FIG. 2A, and when the tool 20 is taken apart, the lead 4 may be broken as shown in FIG. 2B, and the bond strength of the metal bump 5 and the electrode 2 on the semiconductor element 1 is lowered.
Besides, since the temperature of the tool 20 is high, the Sn 4a used for surface treatment on the lead 4 deposits on the bottom of the bonding tool 20 when bonding, and it is oxidized due to high temperature to form a layer poor in thermal conduction, which impairs the thermal conduction from the bottom of the bonding tool 20 to the lead 4, so that the temperature at the junction of the metal bump 5 and electrode 2 may be unstable. As a result, alloy formation state becomes unstable, and the reliability of the bond strength is lowered.
In another method it is possible to heat the stage 24 to about 150.degree. C. and prevent the lead 4 and electrode 2 from becoming cool when pressurizing the tool 20, but the problems of fusion of tool and lead and deposit of Sn on the tool 20 are not solved.
Incidentally, the transfer bump method was disclosed in U.S. Pat. No. 4,494,688 (Hatata).